The Staphylococci make up a medically important genera of microbes known to cause several types of diseases in humans. S. aureus is a Gram positive organism which can be found on the skin of healthy human hosts and it is responsible for a large number of bacteremias.
S. aureus has been successfully treated with the penicillin derivative Methicillin in the past, but is now becoming increasingly resistant (MRSA—Methicillin Resistant S. aureus) to this antibiotic [Harbath et al., (1998) Arch. Intern. Med. 158:182-189]. For example, S. aureus endocarditis mortality can range from 26-45%, and combined β-lactam/aminoglycoside therapy is proving increasingly ineffective in disease eradication [Røder et al., (1999) Arch. Intern. Med. 159:462-469].
It is no longer uncommon to isolate S. aureus strains which are resistant to most of the standard antibiotics, and thus there is an unmet medical need and demand for new anti-microbial agents, vaccines, drug screening methods, and diagnostic tests for this organism. Antibiotics can be grouped into broad classes of activities against surprisingly few targets within the cell. Generally, the target molecule is a cellular protein that provides an essential function. The inhibition of activity of the essential protein leads either to death of the bacterial cell or to its inability to proliferate. Critical cellular functions against which antibiotics are currently in use include cell wall synthesis, folate and fatty acid metabolism, protein synthesis, and nucleic acid synthesis.
A proven approach in the discovery of a new drug, referred to as target-based drug discovery to distinguish it from cell-based drug discovery, is to obtain a target protein and to develop in vitro assays to interfere with the biological function of the protein. Nucleic acid metabolism is essential for all cells. The DNA synthesis machinery includes a number of proteins that act in concert to achieve rapid and highly processive replication of the chromosome in bacteria [reviewed in Kornberg, A., and Baker, T. A. 1992, DNA Replication, Second edition, New York: W.H. Freeman and Company, pp. 165-194; Benkovic, S. J. et al., 2001, Ann. Rev. Biochem. 70: 181-208]. As described below for DNA polymerase III, biological machines are often comprised of multiprotein complexes. Coordinated interactions among proteins of the bacterial primosome and replisome are essential to their efficiency. Thus, any members of essential multiprotein complexes are hypothetical targets for drug development. However, the fact that a protein can be associated with a certain biological function does not necessarily imply that it represents a suitable target for the development of new drugs [Drews J. 2000, Science 287:1960-1964]. For instance, although DNA replication is a well-known and essential process for bacterial growth, only a relatively small number of DNA replication proteins are targeted by currently-available antibiotics. Importantly, screening of compounds for those that inhibit the function of a target must be preferably rapid and selective.
There thus remains a need to identify new bacterial targets and new target domains, and more particularly S. aureus bacterial targets which could be used to screen for and identify antibacterial and more particularly anti-S. aureus agents. There also remains a need to identify new antimicrobial agents, vaccines, drug screening methods and diagnosis and therapeutic methods.
The present invention seeks to meet these and other needs.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.